分离式螺旋热管管外融冰放冷特性分析

在提出分离式螺旋热管蓄冷空调系统的基础上,建立了螺旋热管管外融冰放冷过程的理论模型;分析了蓄冷桶内融冰量及放冷量随时间的变化关系。研究结果表明,在蓄冷桶进口水温一定的情况下,外融冰的循环水流量越大,其融冰放冷过程就越快;在外融冰循环水流量一定的情况下,放冷过程随蓄冷桶进口水温的升高而加快。     

内外融冰技术相结合的蓄冷方式研究

在分别介绍内融冰、外融冰技术的基础上 ,提出采用内外融冰技术相结合的蓄冷方法。该方法能有效克服单融冰方式在空调高峰期释冷能力不足的缺点 ,同时能降低蓄冷设备的设计容量 ,减少一次性投资 ,是一项值得推广应用的技术。     

微重力下套管式蓄冰器的充释冷特性分析

提出了一种可用于航天器热控系统的套管式蓄冰装置,采用热焓法对蓄冷装置的充释冷特性进行了数值模拟,给出了蓄冰装置在充释冷过程中蓄冷介质温度、结融冰厚度和对应充释冷功率随时间的变化,并对不同参数下的计算结果进行了分析比较,可为蓄冷装置的优化设计提供参考。     

直接蒸发式冰蓄冷空调的蓄冰槽融冰强化换热

现有的直接蒸发式冰蓄冷空调蓄冰槽内在融冰运行时都存在不利于传热的较大垂直温差.本文通过在蓄冰槽中下部位置处设置水平交叉盘管,使蓄冰槽内的坚直冰柱易于断裂,从而改善槽内自然对流条件,达到强化换热的目的.实验表明,水半盘管的布置明显减小了蓄冰槽内在融冰过程中的上下层温差,传热过程得到强化,融冰速度加快,制冷系统的COP也相应得到提高.     

球形堆积床蓄冷空调系统实验性能研究

文中对球形堆积床蓄冷空调系统的蓄冷和放冷特性进行实验研究。在实验过程中,测量堆积床内流体温度、蓄冷时蒸发器进出口温度、放冷时换热器进出口温度以及室内机组进风和出风温度。通过测量的数据,得出蓄冷和放冷过程中的蓄冷、放冷速率和蓄冷、放冷量随时间的变化。在放冷时,出风温度稳定在16℃。因此,该系统可以用于空调系统的蓄冷和放冷过程,既有利于电力负荷"移峰填谷",又能满足室内温度调节的需求。     

蓄冷罐式冷板冷藏车厢设计及温度场分析

针对机械式冷藏车和传统冷板冷藏车的缺点,设计蓄冷罐式冷板冷藏车厢,以提高蓄冷式冷藏车的蓄冷量,延长冷藏运输时间。通过计算冷藏车厢运载时的冷负荷,确定冷板尺寸及蓄冷罐容积等参数;建立蓄冷罐式冷板冷藏车厢模型,通过模拟得到冷藏车厢内温度场分布。结果表明,车厢底面隔热层厚度为90 mm时,车厢内货物温度可维持在281.15 K以内,车厢底部温度随运输时间增加逐渐升高,10 h时车厢底面货物温度升至283.75 K;当隔热层厚度增加至150 mm时,车厢底部温度随运输时间增加变化较小,10 h时车厢底面货物温度升至282.58 K。     

冰盘管密度对蓄冷槽取冷特性影响的实验研究

通过构建高密度直接蒸发式冰盘管实验台,研究了不同冰盘管密度对取冷特性的影响。实验结果表明:随着蓄冷槽中冰盘管密度的增大,可使直接蒸发式蓄冰槽取冷水温进一步降低,取冷速率进一步提高,从而能更好地满足低温送风空调系统的要求及空调高峰负荷变化的需要。     

大温差离心机组低负荷运行防喘振策略分析

稳态强磁场实验装置水蓄冷系统是国内外具有代表性的大流量大温差水蓄冷系统之一. 系统包含两个3000 m3 的蓄水罐, 为提升蓄冷量双罐均采用了自然分层技术. 由于该技术的特性, 在蓄冷后期, 离心式冷水机组的入口水温会偏低, 这导致系统新增的12 ℃ 大温差机组在试运行阶段多发低负荷喘振故障, 影响了制冷运行的稳定度. 本文首先对离心式冷水机组的喘振机理进行了阐述, 进而分析了在改造前针对该台冷水机组所做的防喘振优化措施; 通过热气旁通改造结合相关参数的合理设置, 避免机组喘振风险; 通过优化 DDC 控制, 优化机组减载能力, 避免了低负荷振动及噪声. 本次改造为系统的安全稳定运行提供了保障.     

蓄冷球堆积床动态充冷性能模拟

根据蓄冷球和载冷剂之间的能量平衡,建立了蓄冷球堆积床充冷过程的数理模型。该模型考虑了载冷剂与蓄冷球之间的换热系数变化、载冷剂的导热、相变蓄冷材料的过冷度以及蓄冷球堆积床热损失的影响。采用数值计算方法模拟了蓄冷球堆积床的充冷过程,讨论了载冷剂入口温度、初始温度和流速对充冷过程蓄冷材料温度、载冷剂温度和蓄冰率的影响。     

一种蓄冷式飞机地面空调车系统性能的研究

针对传统的飞机地面空调车存在不能以小功率用电保障大功率需求及冷量损失严重等问题,提出一种相变蓄冷式飞机地面空调车,简要分析了系统组成及其原理,对蓄、释冷系统进行了实验研究.结果表明:蓄冷工况下相变蓄冷材料在-2℃开始相变,蓄冷量达到200 kW时耗时38 min,蓄冷3 h蓄冷量为950 kW;释冷工况下蓄冷箱的释冷时...     

制冰方式的研究

文中提出一种新型的浸润式动态制冰方式,并利用数值模拟的方法对新型制冰方式和传统滑落式制冰方式进行了对比研究。结果表明,在制冰时间相等的条件下,新型制冰方式的制冰量提高了约19%。在制冰量相等的条件下,制冰周期平均缩短了10分钟,蓄冰周期平均缩短了约2.3小时。此外,新型制冰机组采用的脱冰方式可以减小冷凝器的换热面积。     

冰浆储存与融化及流动换热特性研究现状及展望

冰浆具有良好的流动性、传输性以及传热性能,在电力削峰填谷上有着很大的应用前景。文中主要对冰浆制取方式的优劣性进行对比,着重介绍了国内外冰浆储存与融化的研究进展,对冰浆流动换热的动态特性进行分析,并根据研究现状对下一步研究工作进行了展望。     

冰蓄冷低温送风空调系统风管管路分析研究

研究得出冰蓄冷低温送风空调系统较常规空调系统在风管管路阻力及风管截面积的优越性。依据管路阻力计算公式利用VB语言编写风管比摩阻的计算程序,并利用该计算程序对相同工况下的典型的低温送风温度与常规送风温度的比摩阻进行计算,进而得到风管管路阻力,同时计算得出各送风温度下的风管截面积,并进行对比分析。相同计算条件下,冰蓄冷低温送风空调系统的风管沿程阻力是常规送风系统的40%—70%;采用8℃低温送风方式时,其风管截面积较常规空调可减少20%—30%。与常规空调系统相比,采用冰蓄冷低温送风空调系统可明显减小风管的沿程阻力和截面积,大大降低了风机耗能和建筑层高,节省了运行及建材费用。     

Universality class of the fiber bundle model on complex networks

We investigate the failure characteristics of complex networks within the framework of the fiber bundle model subject to the local load sharing rule in which the load of the broken fiber is transferred only to its neighbor fibers. Although the load sharing is strictly local, it is found that the critical behavior belongs to the universality class of global load sharing where the load is transferred equally to all fibers in the system. From the numerical simulations and the analytical approach applied to the microscopic behavior, it is revealed that the emergence of a single dominant hub cluster of broken fibers causes the global load sharing effect in the failure process.     

Hot water heat accumulators in single-family houses

In Sweden, as in many other countries, there is a significant difference in electricity demand between day and night. In order to encourage the end use consumer to use less electricity during peak situations, time-of-use tariffs have become more common. The price differs from about 0.8 to 0.35 SEK/kWh, taxation included. (1ECU equals about 7 SEK.) If some of the electricity under the high price period, which falls between 0600 and 2200 during November to March, could be transferred to the low price hours, the electricity bill could be reduced. In Sweden it is common to use electricity for space and hot water heating, at least in single-family houses. By use of a hot water accumulator the need for heat could be produced during the cheap hours and the storage could be discharged when the high price hours occur. This paper describes the electricity use for hot water and space heating in a single-family house sited in Linköping, Sweden, where extensive monitoring has been utilized during 1987. Some 30 values for temperatures and electricity demands have been measured each hour, or sometimes even for shorter time intervals. These monitored data have been the base for examining if a water accumulator could be of interest for the proprietor of the building, i.e. if the cost for the accumulator is less than the money saved by the reduced electricity cost.     

The Local Structure of Globalization

We study the evolution of the network of foreign direct investment (FDI) in the international electricity industry during the period 1994–2003. We assume that the ties in the network of investment relations between countries are created and deleted in continuous time, according to a conditional Gibbs distribution. This assumption allows us to take simultaneously into account the aggregate predictions of the well-established gravity model of international trade as well as local dependencies between network ties connecting the countries in our sample. According to the modified version of the gravity model that we specify, the probability of observing an investment tie between two countries depends on the mass of the economies involved, their physical distance, and the tendency of the network to self-organize into local configurations of network ties. While the limiting distribution of the data generating process is an exponential random graph model, we do not assume the system to be in equilibrium. We find evidence of the effects of the standard gravity model of international trade on evolution of the global FDI network. However, we also provide evidence of significant dyadic and extra-dyadic dependencies between investment ties that are typically ignored in available research. We show that local dependencies between national electricity industries are sufficient for explaining global properties of the network of foreign direct investments. We also show, however, that network dependencies vary significantly over time giving rise to a time-heterogeneous localized process of network evolution.     

Time resolved spectroscopic NMR imaging using hyperpolarized 129Xe

We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized 129Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol.     

Artificial square ice and related dipolar nanoarrays

We study a frustrated dipolar array recently manufactured lithographically by Wang in order to realize the square ice model in an artificial structure. We discuss models for thermodynamics and dynamics of this system. We show that an ice regime can be stabilized by small changes in the array geometry; a different magnetic state, kagome ice, can similarly be constructed. At low temperatures, the square ice regime is terminated by a thermodynamic ordering transition, which can be chosen to be ferro- or antiferromagnetic. We show that the arrays do not fully equilibrate experimentally, and identify a likely dynamical bottleneck.     

基于吸附制冷的微型冷热电联供系统实验研究

设计并建成一套小型燃气内燃机和高效余热吸附制冷机相结合的微型冷热电联供实验系统,对其在不同工况下的运行参数和特性进行实验研究,分析了联供系统的节能经济性。联供系统可以同时提供峰值发电量12kW,峰值制冷量9kW或峰值供热量28kW。结果表明联供系统热电联供节能性优于冷电联供,热电联供一次能源利用率均在70%以上.当天然气价格为1.8元/Nm~3和电价0.61元/kWh时,系统投资回收期低于4年.     

Time resolved spectroscopic NMR imaging using hyperpolarized Xe

We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized ¹²⁹Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol.